The present teachings relate in general to laser diodes. The teachings relate in particular to the combination of radiant power emitted by one or more laser diodes into a beam that can be introduced into a single optical fiber for transport or for other purposes.
Laser diodes are well known in the art as small and useful devices for converting input electrical power to an intense beam of optical or infrared radiation, but their use is constrained in several ways. The output beam is emitted with different angular spread and different apparent source size in two perpendicular axes, and may need to be reshaped for practical applications. A laser diode also heats its supporting structure when it is used. The damage threshold of a laser diode's output surface limits its maximum power. Many applications, such as welding, surgery, and optical pumping of the active core of a fiber laser are facilitated by various techniques of combining the outputs of a plurality of laser diodes into a single beam, to be input to an optical fiber. In one such technique, each emitted diode laser beam was pre-shaped by an attached microlens and eight separately mounted diodes were provided with lenses and supported in a metal base frame. The beams were then combined by reflection from a polyhedral mirror and brought to a collective focus into an optical fiber. The total beam power provided was 32 Watts.
Efforts to put higher radiant power from a plurality of laser diodes into an optical fiber have continued. In late 2003, a three year program to develop Super-High Efficiency Diode laser Sources (SHEDS), with emphasis on high effective power, small size, light weight, and minimal power wasted as heat was started. Few of the stated program goals have been met, so there is a need for a better technique for combining the output beams from laser diodes.
Two organizations have reported a high-power Fiber-Coupled laser-diode Module (FCM) with 200 W or more output, not yet reaching the SHEDS goals for low Size, Weight, And waste Power (SWAP).
The commercially available Fiber-Coupled laser-diode Module (FCM) with the highest power output into a fiber, still only 200 W, has been sold for more than ten years as the LIMO AV-10 series. It is characterized by a power conversion efficiency of only 31% and a weight of about 8 kilograms.